feat: drive RunControlPage provider list from GET /config/providers API

[Ryan-Atkinson87]

Background

PR #227 wired SettingsPage's Default Provider <select> to GET /config/providers so it stays in sync with the ProviderName Literal type automatically.

RunControlPage.tsx still has a hardcoded PROVIDERS constant (used in the run-form provider select). Adding a new adapter and updating ProviderName will surface it in Settings but not in the Run form until this is fixed.

Work

• Fetch /config/providers on RunControlPage mount (parallel-fetch pattern already used in SettingsPage).
• Replace the hardcoded PROVIDERS constant with the API response list.
• Add/update test to assert a dynamic provider appears in the run-form select.

Acceptance criteria

• Provider select in the Run form is driven by the API response, not a constant
• Adding a new ProviderName value surfaces automatically in the Run form
• npm run test -- --run passes
• npm run lint and npm run typecheck clean